The gasification of coal in underground formations is well known. Similarly the extraction of oil by the use of solvents from beds previously considered exhausted, at least to conventional techniques, is now well known. It has been estimated that by normal well drilling operations in a fresh field less than 30% of the deposits can be obtained. Using such methods as injecting water and solvents it has been estimated that another 30 to 35% can be extracted. It appears to be generally agreed that at least 35% of the original material in the oil bed, before the well was drilled, cannot be extracted economically. Although systems have been proposed for extracting and remaining oil these systems are complicated and expensive.
Brandon, in U.S. Pat. No. 2,796,129 seeks to extract oil from an apparently exhausted well by undercutting the formation and by forming horizontal tunnels from which the undercutting can be carried out. The notion in Brandon is to release the capillary lock within the strata causing an outflow of oil, water and gas. However, the formation of a horizontal cut in this matter can be quite complicated and the Brandon method has not found wide application. In particular for each cut three access points are required.
Malloy, in U.S. Pat. No. 3,452,545 shows a method of earth working that is of interest. In Malloy an endless chain is carried by standards and winches. However, Malloy is a means of cutting down into the ground from the surface, that is in a direction different from that required by the art to which the present invention relates.
The present invention seeks to provide a method of preparing an underground bed for treatment by forming easily and relatively cheaply large numbers of substantially vertical fissures in that underground formation to facilitate in particular the saturation of the formation with a solvent. However, it is also applicable to the gasification of coal, to the steam extraction of an oil formation and to the use of combustion and high pressure water injection as a means of forcing the oil out of an apparently exhausted formation.